Alma 5:48 in the current text of the Book of Mormon reads:
And
I say unto you, that I know of myself that whatsoever I shall say unto you,
concerning that which is to come, is true; and I say unto you, that I know that
Jesus Christ shall come, yea, the Son, the Only Begotten of the Father, full of
grace, and mercy, and truth. And behold, it is he that cometh to take away the
sins of the world, yea, the sins of every man who steadfastly believeth on his
name.
The printer’s manuscript and the
1830 edition of the Book of Mormon do not read “the Son, the Only Begotten of
the Father,” but “the son of the only begotten of the Father.”
Skousen notes that:
The
extra of after Son appears to be an early error in the
transmission of the text (either when the scribe in [the Original Manuscript]
took down Joseph Smith's dictation or when the scribe 2 of [the Printer's
Manuscript] copied the text from [the Original Manuscript]. The same error
appears later on in the book of Alma:
Alma
13:9
thus
they become high priests forever
after
the order of the son [of>js Null 1 [of A] BCDEFGHIJKLMNOPQRST]
the
Only Begotten of the Father
In
both cases, scribe 2 of [the Printer's Manuscript] was the one who copied the
text from [the Original Manuscript] into [the Printer's Manuscript]. Joseph
Smith, in his editing for the 1837 edition, deleted the extra of in both
these passages. Literally, the earliest text for these two passages says that
there is a son of the Son of the Father, which contradicts all other uses in
the Book of Mormon of the phrases "Only Begotten Son" and "Only
Begotten of the Father". Otherwise, these phrases always refer to the Son
of God, not to a son of the Son of God . . . (Royal Skousen, Analysis of Textual
Variants of the Book of Mormon, Part 3: Mosiah 17-Alma 20, pp. 1698-99)
Skousen then references 2 Nephi
25:12; Jacob 4:5; 4:11; Alma 9:26; 12:33; 12:34; 13:5 where Jesus is "the
Only Begotten Son" or "Only Begotten of the Father."
Gardner agrees with Skousen that
this is probably an error:
I
suspect that the original was “the son, the only begotten of the Father” just as
it has been edited since the 1837 edition. (Brant A. Gardner, Second
Witness: Analytical and Contextual Commentary on the Book of Mormon, 6
vols. [Salt Lake City: Greg Kofford, 2007], 4:109)
Either way, Alma 5:48 is a great text showing that the Book of Mormon does not Modalism. On the charge that early Latter-day Saint theology was that of Modalism, see, for e.g.:
Early Mormon Modalism? A Dialogue with Stephen Murphy
See also my two-part debate/dialogue with my friend Adam Stokes on whether the Book of Mormon and other early Restorationist texts (e.g., Lectures on Faith; 1832 First Vision Account) taught Modalism.